Anionic Host Research Articles

The rational design of anion host compounds: an exercise in subtle energetics.

Lock-and-key binding is an inadequate description for the molecular-recognition interaction of guanidinium cations and carboxylates in acetonitrile (see picture) as shown by direct calorimetric determinations in a tailored series of host–guest pairs.

Computational and experimental studies of di- and tetrasubstituted calix[4]arenes.

Calixarenes are molecular bowls or baskets that have been demonstrated to serve as hosts for cations, anions, and neutral molecules. The central cavity and scaffolding of various functionalities on the upper and lower rims establishes this class of compounds as extremely important in supramolecular chemistry studies. In earlier studies, calixsugars (molecules that have sugar molecules appended to the upper rim of the calix) were prepared. Among the potential advantages of these molecules are increased water solubility and enhanced possibilities that these chiral attachments can promote enantiomeric selection. Computational studies, however, have indicated that the chosen calixsugars had significantly encumbered upper rims, suggesting that host-guest associations would be limited. In an attempt to understand those factors responsible for the favored conformations of calixsugars, a number of 5,17-disubstituted and tetrasubstituted calix[4]arenes were prepared and studied experimentally as well as by molecular mechanics conformational searching techniques.

Protonated bis(quinuclidine) included in layered bis(urea)–bromide and -iodide hosts: new ternary urea inclusion compounds

The synthesis, crystal structure, and properties of novel ternary inclusion compounds formed by the insertion of protonated bis(quinuclidine) guests into urea–bromide and urea–iodide anionic hosts are reported. (Urea2[quinuclidine2H]+Br−), 1, and (urea2[quinuclidine2H]+I−), 2, are monoclinic, space group C2. The cell parameters for 1 are a = 19.323(8), b = 7.145(3), c = 8.566(4), β = 112.19(3), dcalc = 1.284 and Z = 4, considering 472 reflections; for 2 they are a = 20.51(11), b = 7.34(3), c = 8.17(4), β = 111.81(8), dcalc = 1.369, Z = 4, considering 716 reflections. In the two structures each urea molecule interacts with adjacent urea molecules via N–H⋯O hydrogen bonds forming a ribbon-like arrangement. The ribbons are linked through halide ions by N–H⋯X hydrogen bonds forming layered structures. The distances between the layers are 10.301 A for 1 and 8.566 A for 2. The compounds may be described as commensurate species. Conductivity values determined for 1 and 2 at room temperature are 1.19 × 10−5 and 8.66 × 10−7 (Ω cm)−1, and they increase with temperature. Aspects of the thermal stability of the products are discussed.

Design and synthesis of preorganized tripodal fluororeceptors based on hydrogen bonding of thiourea groups for optical phosphate ion sensing

Expecting a preorganization effect, tripodal anion host molecules were designed and synthesized. It was demonstrated that two kinds of new thiourea derivatives having a six-fold substituted benzene ring as a preorganized spacer were effective for recognition of the tetrahedral dihydrogen phosphate anion. A tripodal fluororeceptor 1 having a pyrene moiety adjacent to the thiourea binding site showed long-wavelength emission upon addition of guest anions in acetonitrile. On the other hand, a tripodal thiourea receptor 2 connected to anthracene groups via methylene units showed a decrease in fluorescence intensity upon addition of anions. In both cases, the degree of the change in emission intensity was in the order of H2PO4− > CH3COO− > Cl− ≫ ClO4−, which is clearly different from that of reference compounds having only one binding site. Association constants (Ka) of these tripodal fluororeceptors also confirmed the dihydrogen phosphate selectivity over the more basic acetate anion in this homogeneous solution system. The characteristics of the fluororeceptors using the preorganization effect were shown to be promising for the development of chemical ion sensors with a specific anion selectivity.

J-Aggregates Granting Giant Second-Order NLO Responses in Self-Assembled Hybrid Inorganic–Organic Materials

Huge second harmonic generation (SHG) activityis displayed by the new hybrid inorganic–organic material [DAMS*][Cu5I6] (see Figure). Ab-initio XRPD structure determination explains this through the presence of cationic guest J-aggregates between Cu-defective anionic host CuI slabs. Thermal stability and thin-film suitability make the material technologically interesting.

J-Aggregates Granting Giant Second-Order NLO Responses in Self-Assembled Hybrid Inorganic-Organic Materials

Huge second harmonic generation (SHG) activityis displayed by the new hybrid inorganic–organic material [DAMS*][Cu5I6] (see Figure). Ab-initio XRPD structure determination explains this through the presence of cationic guest J-aggregates between Cu-defective anionic host CuI slabs. Thermal stability and thin-film suitability make the material technologically interesting.

Temperature, solvent, proton transfer and complexation effects on the conformational flexibility of the anionic host calix[6]arenesulfonate

Calix[6]arenesulfonate is a flexible host that adopts the 1,2,3-alternate conformation in DMSO- d 6 solution at room temperature, as evidenced by 1H NMR spectroscopic data. This conformational preference is lost at higher temperatures or in the presence of acid. In aqueous media this calixarene exhibits a very simple proton NMR spectrum, reflecting the fast exchange between several conformations. Electrochemical data obtained with electroactive guests (ferrocenemethanol [FcOH], ferrocenylmethyldimethylammonium [FcN +Me 3], and cobaltocenium [Cob +]) indicate that the anionic calixarene host forms complexes with all of them. The stability of the corresponding complexes increases with the number of positive charges on the guest, but the uncharged forms of the guests are also bound. The affinity between the calixarene and the ferrocene-containing guests decreases substantially as the solution goes from neutral (pH 7.0) to acidic (pH 2.6). 1H NMR spectroscopic data in neutral aqueous solution suggests that the calixarene ( 1 8−) adopts the 1,2,3-alternate conformation as it forms very stable ternary complexes with either two Cob + or two FcN +Me 3 guests, respectively. The complex with FcOH is weaker. Overall, our data demonstrate that the conformational state of this anionic calixarene host is strongly affected by the nature of the solvent, pH, temperature, as well as by the presence of appropriate guests in the solution.

Self-assembly of frameworks with specific topologies: construction and anion exchange properties of M3L2 architectures by tripodal ligands and silver(I) salts.

Three five-component architectures, compounds 3, 4, and 5 were obtained by self-assembly of tripodal 1,3,5-tris(imidazol-1-ylmethyl )-2,4,6-trimethylbenzene (6) and 1,3,5-tris(benzimidazol-2-ylmethyl)benzene (7) ligands with silver(I) salts. The structures of these novel complexes have been determined by X-ray crystallography. The results of structural analysis indicate that these frameworks have same M3L2 components, but different structures. Compounds 3 and 4 are both M3L2 type cage-like complexes, while the 5 is an open trinuclear complex. The complex 3 is a cylindrical cage with simultaneous inclusion of a perchlorate anion inside of the cage as a guest molecule. Such guests can be exchanged for other anions through the open edge of the cage as evidenced by crystal structure of 4. The results demonstrate that the molecular M3L2 type cage can act as a host for anions and provide a nice example of supramolecular architectures with interesting properties and possible applications.

Chiral recognition of dipeptide methyl esters by an anionic beta-cyclodextrin.

Chiral recognition of dipeptide methyl esters by anionic heptakis[6-carboxymethylthio-6-deoxy]-beta-cyclodextrin (per-CO(2)(-)-beta-CD) was studied in D(2)O at pD 7.0 by means of (1)H NMR spectroscopy. The methyl esters of alanylalanine (Ala-Ala-OMe), alanylleucine (Ala-Leu-OMe), alanyltryptophan (Ala-Trp-OMe), glycyltryptophan (Gly-Trp-OMe), valyltryptophan (Val-Trp-OMe), leucyltryptophan (Leu-Trp-OMe), and tryptophylalanine (Trp-Ala-OMe) were used as the dipeptides. The binding constant (K) determined from NMR titration increases in the order Ala-Ala-OMe < Ala-Leu-OMe < Ala-Trp-OMe, suggesting that van der Waals interactions between the host and the guest participate in complexation. Coulomb interactions between the protonated dipeptide methyl esters and the anionic host seem to be another attractive force. Per-CO(2)(-)-beta-CD interacts with the (R,R)-enantiomers of the dipeptide methyl esters more strongly than the (S,S)-enantiomers. Such enantioselectivity corresponds to that for alpha-amino acid methyl esters such as Leu-OMe and Trp-OMe, whose (R)-enantiomers are the preferable guests. The enantioselectivity is mainly dominated by amino acid residue at the C-terminal and chirality at the N-terminal residue plays an assistant role. An asymmetrically twisted shape of the host cavity may be essential for chiral recognition.

Attenuation of Hofmeister bias in ion-pair extraction by a disulfonamide anion host used in strikingly effective synergistic combination with a calix-crown Cs+ host.

A calix-crown/disulfonamide dual-host combination in 1,2-dichloroethane exhibits markedly enhanced ion-pair extraction of caesium salts, with the observed synergism following an anti-Hofmeister order.

Novel Anionic Host Lattices Built of Squarate and Thiourea Molecules

The new inclusion complexes [(C2H5)4N+]2C4O42−·4(NH2)2CS·2H2O (1), [(C2H5)4N+]2C4O42−·6(NH2)2CS (2) and [(C2H5)4N+]2C4O42−·2(NH2)2CS·2H2O (3) have been prepared and characterized by X-ray crystallography. In the crystal structure of (1), infinitely extended squarate–water chains inter-link adjacent puckered thiourea layers to generate a three dimensional host lattice with large uni-directional rectangular channels each containing a double column of well-ordered tetraethylammonium cations. In complex (2), well-ordered tetraethylammonium cations are stacked in single columns within the channel-type thiourea-squarate host lattice constructed by the cross-linkage of two types of layers. In complex (3), well-ordered teteraethylammonium cations are sandwiched between puckered layers generated by the cross-linkage between zigzag (C4O42−·2H2O)∞ chains and singly hydrogen-bonded dimeric thiourea ribbons.

Isostructurality in inclusion compounds based on interchangeability of equivalent synthons in a hydrogen-bonded host lattice

The new inclusion complex bis(tetra– n–propylammonium) squarate–urea–water (1/6/2), [( n–C 3H 7) 4N +] 2C 4O 4 2−·6(NH 2) 2CO·2H 2O, has a three-dimensional anionic host framework containing large uni-directional channels that accommodate the hydrophobic cations. Replacement of its dumbbell-shaped hydrogen-bonded moiety (H 2O–C 4O 4 2−–H 2O) by the equivalent synthon (H 2O–Br −) 2 generates the known crystal structure of ( n–C 3H 7) 4N +Br −·(NH 2) 2CO·H 2O, thereby providing an interesting example of isostructurality in the realm of inclusion compounds.

Channel- and layer-type anionic host structures in inclusion compounds of urea, tetraalkylammonium terephthalate/trimesate and water

New crystalline adducts of tetraalkylammonium terephthalate/trimesate with urea and water molecules result from hydrogen-bond directed assembly of complementary acceptors and donors, and the anionic host lattices are described using the graph-set notation to identify distinct hydrogen-bonding motifs and patterns. Tetra-n-butylammonium terephthalate-urea-water (1/6/2), C46H104N14O12 (1), triclinic, space group P1, a = 8.390 (2), b = 9.894 (2), c = 18.908 (3) A, alpha = 105.06 (2), beta = 94.91 (1), gamma = 93.82 (2)o, Z = 1, is composed of hydrogen-bonded terephthalate-urea layers, which are intersected by urea layers to generate a three-dimensional network containing large channels for accommodation of the cations. Tetraethylammonium terephthalate-urea-water (1/1/5), C25H58N4O10 (2), triclinic, P1, a = 9.432 (1), b = 12.601 (1), c = 14.804 (1) A, alpha = 79.98 (1), beta = 79.20 (1), gamma = 84.18 (1)o, Z = 2, has cations sandwiched between hydrogen-bonded anionic layers. Tetraethylammonium trimesate-urea-water (1/2/7.5), C35H86N7O15.5 (3), triclinic, P1, a = 13.250 (1), b = 14.034 (1), c = 15.260 (1) A, alpha = 72.46 (1), beta = 78.32 (1), gamma = 66.95 (1)o, Z = 2, manifests a layer-type structure analogous to that of (2). Tetra-n-propylammonium hydrogen trimesate-urea-water (1/2/5), C35H78N6O13 (4), orthorhombic, Pna2(1), a = 16.467 (3), b = 33.109 (6), c = 8.344 (1) A, Z = 4, features hydrogen trimesate helices in a three-dimensional host architecture containing nanoscale channels each filled by a double column of cations.

(Ethylenediamine)Pt(uracilate)]4 – A Metal Analogue of Calix[4]arene: Coordination Chemistry of Its 1,3-Alternate Conformer towards First-Row Transition-Metal Ions

The open “molecular box” [(en)Pt(U-N,N)]4 (1) (where en = structurally characterized heteronuclear compounds show a 1,3-alternate arrangement of the uracil nucleobases. Pt–M ethylenediamine, U = uracil dianion) is able to act as an efficient ligand for additional metal ions. Reactions of the 1,3contacts are in the range 2.743(2)–2.804(2) A; the Pt atoms act as weak σ donors to the heterometals. In spite of the high alternate conformer of 1 with divalent metal ions result in the formation of octanuclear compounds of the general formula degree of positive charge associated with compounds 2a–5, they do not behave as hosts for anions. This is a consequence [(en)Pt(U-N,N,O,O)M]4X8 [M = Cu2+, X = Cl (2a), X = (SO4)0.5 (2b), and M = Co2+ (3), Ni2+ (4), Zn2+ (5) with X = of the orientation of the four nucleobases which, in contrast to a cone arrangement, does not produce a sufficiently large (SO4)0.5], in which the heterometals are bound at the exocyclic oxygen atoms of the uracil nucleobases. The cavity for the incorporation of anions.

Hydrogen-bonded anionic layer structures constructed from 4,4?-biphenyldicarboxylate and water molecules, and also with urea as an additional component

The crystal engineering of four new layer-type molecular solids is described. The anionic host layer in 2(Et4N+)·[4,4′-(C6H4)2(COO−)2]·4H2O (1) is constructed from 4,4′-biphenyldicarboxylate (BPDC) and a square (H2O)4 cluster through O—H···O and C—H···O hydrogen bonds. A hydrogen-bonded [(H2O)8O4] cluster connects BPDC ions through O—H···O linkages to form an anionic layer in 2[(n-Pr)4N+]·[4,4′-(C6H4)2(COO−)2]·8H2O (2). In 2[(n-Pr)4N+]·[4,4′-(C6H4)2(COO−)2]·2[(NH2)2CO]·4H2O (3) and 2[(n-Bu)4N+]·[4,4′-(C6H4)2(COO−)2]·­2[(NH2)2CO]·4H2O (4), BPDC forms analogous hydrogen-bonding patterns with urea and water molecules through N—H···O and O—H···O interactions, but the resulting anionic layers are pleated and nearly planar, respectively. Tetraalkylammonium cations are sandwiched between layers as guest species in all four structures. Copyright © 2000 John Wiley & Sons, Ltd.

Zwitterionic Guanidinium Compounds Serve as Electroneutral Anion Hosts

The complexation of anions in solvating phases by artificial receptors requires the total or at least partial replacement of their solvation shells by the mutual supramolecular interactions. Supplementing well-known approaches that rely on net electrostatic charges or extensive hydrogen bonding for guest complexation the present work focuses on the alternative concept of charge separation in the host to create a cationic site suitable for strong interaction with negatively charged guests. An anionic moiety balancing the overall host charge to zero is incorporated in a way to prevent collapsing into an ion pair. Using bicyclic guanidinium anchor groups for direct guest binding and a closo-borane cluster as an anionic countercharge the ditopic zwitterionic host 17 was designed and prepared in a convergent synthetic scheme. Despite its electroneutrality 17 binds inorganic and organic oxoanions such as sulfate, oxalate, squarate and p-nitrophenyl phosphate with affinity constants reaching 3.1 × 104 M-1 in DMS...

A new layer type anionic host lattice constructed from urea, squarate, bicarbonate, and water molecules

A new inclusion complex bis(tetraethylammonium) squarate-tetraethylammonium hydrogen carbonate-urea-water [(C2H5)4N+ ]2C4O2-4 — 2(C2H5)4N+ HCO-3 — 4(NH2)2CO-6H5O has been prepared and characterized by X-ray crystallography. Crystal data: MoKα radiation, space group P21ln (No. 14), a = 12.283(2), b= 17.287(3), c= 14.898(3) a, υ= 101.27(3)0, Z= 2, R1= 0.055 for 3634 observed MoKα data. In the crystal structure of the title compound, cross linkage between hydrogen-bonded zigzag ribbons of the types [(urea)4(H2O)2]∞ and [(C4O2-4)(H2O)2(HCO-3)2(H20)2]∞ generates urea-anion host layers, with both well-ordered and disordered tetraethylammonium cations occupying the space between them.

Hybrid Materials Formed by Two Molecular Networks. Towards Multiproperty Materials

The possibilities offered by hybrid materials formed by two molecular networks in the context of the molecular magnets are illustrated. Molecule-based layered magnets are used as anionic hosts for electroactive molecules, with the aim of obtaining multiproperty materials exhibiting in addition to the cooperative magnetism other interesting properties according to the nature of the inserted molecules. In particular, hybrid molecular compounds containing molecular species giving rise to paramagnetic, conducting, or bi-stable properties are reported.

Ferrocene and Silicon Containing Organotin (IV) Halides as Lewis Acidic Hosts for Anions

Ferrocene and Silicon Containing Organotin (IV) Halides as Lewis Acidic Hosts for Anions

Hybrid molecular magnets incorporating organic donors and other electroactive molecules

Molecule-based bidimensional ferromagnets can be used as anionic hosts for electroactive molecules, with the aim of obtaining multiproperty materials exhibiting in addition to the cooperative magnetism other interesting properties according to the nature of the inserted molecules. In particular, hybrid molecular compounds containing conducting (TTF-type organic donors), bi-stable or non-linear optical species are reported.